Preheat the oven to 325°F. Grease a 9-inch glass or ceramic pie plate with soft unsalted butter. Line it with a circle of parchment paper and grease it as well.
In a large bowl, whisk together the eggs, coconut milk, stevia, and vanilla extract with a hand whisk.
Use a fine-mesh strainer to gradually sift in the cocoa powder. Whisk until smooth, scraping the sides of the bowl with a rubber spatula as needed.
Whisk in the coconut flour, then the salt and baking powder.
Pour the mixture into the prepared pie plate. Bake it for 15 minutes.
Carefully place foil strips along the pie's edges to prevent overbaking. Continue baking until the center is still jiggly but not completely liquid, about 10 more minutes.
Cool the pie for 2 hours in the pan on a wire rack, then for 2 more hours in the fridge before slicing.
This pie is not for you if you like your baked goods very sweet. Its sweetness profile resembles 90% cacao chocolate. It's more "rich and chocolaty" than "sweet."
To slice the pie, use a sharp, non-serrated knife. Run the blade under very hot water and carefully wipe it with a clean kitchen towel between cuts. This will help prevent the knife from sticking and tearing the pie.
You can keep the leftovers in an airtight container in the fridge for up to a week. Remove them from the fridge at least 30 minutes before enjoying them. You can also freeze the cooled leftovers for up to three months.